The present invention relates to a combination rotary and linear motor which uses a modified brushless DC motor.
There are a number of different configurations which provide a combination of rotary and linear motion. U.S. Pat. No. 4,570,254 issued to Agostini discloses a drive motor for a compact disc player which uses permanent magnets for both the rotor and the stator and employs magnetic attraction to move the rotor from an intermediate position to a playing position. The use of an axial magnetic attractive force results in a movement, which requires external stops to achieve a final position, as there is no control over the force itself.
There are a series of patents represented by U.S. Pat. No. 5,627,418 issued to Satomi et al. which employ a stepping motor having a stator and a mover having a series of laminated iron plates shaped to provide inner stator teeth along a direction of the motor axis and teeth in the circumferential direction and outer mover or rotor teeth opposed to said stator teeth. Permanent magnets are incorporated into the stator or rotor. Energizing the stator causes rotary motion and stepped linear motion. Aside from being complex to produce, such motors do not provide continuous precise motion control.
U.S. Pat. No. 3,394,295 issued to Cory discloses a pair of diametrically opposite coils which operate in conjunction with an axially spaced apart pair of diametrically opposite permanent magnets oriented at 90 degrees to the coils. The rotor has discrete energized positions which are 90 degrees with respect to each other and so also do not provide precise angular control.
Accordingly, it is an object of the invention to provide an improved motor providing concurrent rotary and linear motion. It is a further object of the invention to provide a motor with both concurrent rotary and linear motion and both of which are continuously precisely controllable.
According to the invention there is provided a rotary and linear motor having a rotor, a casing and a plurality of stator coils mounted to the interior of the casing spaced from the rotor and radially spaced apart around the rotor. A rotary and linear motor control circuit is operative to receive input data signals and to process these data signals so as to produce a plurality of pulse width modulated output control signals. A multi-phase inverter circuit is coupled to an output of the rotary and linear motor control circuit and is responsive to the plurality of output control signals to drive the stator coils and produce a desired z-axis displacement, z, and rotor angular displacement, xcex8.
The input data signals may include sensed linear displacement, z, sensed rotor angle, xcex8, coil current sensor outputs Ia, and Ib, and command axial displacement, Zc, and command rotary angle, xcex8c.
In another aspect of the invention there is provided a method of controlling the linear and rotary movement of a motor having a plurality of stator coils radially spaced around a rotor, wherein the rotor has at least one magnetic pole. The method includes transforming the coil currents through the stator coils into a current, Id, through a notional coil having a d-axis parallel to a pole of the rotor and a current, Iq, through a notional coil having a q-axis perpendicular to the d-axis. Next the method involves employing current Id to control the angular position of the rotor and employing current Iq to control the linear position of the rotor.